Process for treating metals



April 12, 1938. J. o. BETTERToN ET Al. l 2,113,543

PROCESS FOR TREATING METALS Filed May 27, 1935 475 4 lNvr-:NToRs ATTORNEY Patented Apr. 12, 1938 l UNITED STATES PATENTI OFFICE PROCESS FOB. TBEATING METALS Application May 27, 1935, Serial No. 23,517

12 Claims.

In accordance with the present invention. there is provided animproved process for separating tin from tin containing alloys, especially tinlead alloys and lead alloys containing tin.

In salvaging scrap lead and drosses arising from various alloying procedures, lead and lead alloys containing substantial amounts of tin are produced. While it is usually a fairlysimple matter 'to remove tin from these alloys by oxidation, such procedure is open to the objection that there is not obtained a clean-cut separation of tin from the lead. Usually a rather large amount of. lead is taken oil with the oxidized dross, and the material produced from this dross is often so rich in lead as to necessitate reconcentration in order to produce a readily salable lead-tin alloy. vIn., addition, certain tin containing alloys oi?y lead such as lead-antimony alloys, for example, are not susceptible to the oxidation procedure for removing their tin content'with- 20 out involving a considerable and undesirable loss of .antimony from the lead, and at the same time producing a tin concentrate relatively rich in antimany, which involves elaborate reprocessing operations in order to make satisfactory separations.

One of the objectsv of the present invention is to provide a process for separating the tin from alloys such as those above mentioned in which the tin is substantially completely removed from the alloy in a simple and direct operation.

A still further object of. the invention is to provide a process for removing tin from leadtin alloys, and tin-containing alloys of lead wherein there is produced a tin' compound substantially` free from other base metals from which a tin of very high purity may be produced.

A still further object of the invention is to provide a process of the above indicated character in which there are avoided anysubstantial loyed with lead.

Other objects of' the invention will appear hereinafter, the novel features and combinations of steps of the new process being -set forth in the appended claims.

The present invention depends upon the facts, first, that tin in the presence of Vlead chloride acts as a reducer for the latter to form stannous chloride in accordance with the reaction and, second, that the resulting stannous chloride is converted into stannic chloride by chlorine gas:

' order to remove the resulting stannous chloride, losses of lead or of any oi.' the usual metals al- The stannic chloride, vbeing volatile at the temperatures employed, passes out from the system.

The first of these reactions is a simpleequilibrium, as indicated above, and the equilibrium point 5 favors a predominance of lead over tin, since the heat of formation of lead chloride is somewhat higher than that of stannous chloride. Therefore, when it is attempted to carry out the above reaction, only a small amount of tin will react with lead chloride to form stannous chlo-` ride; if, however, the tin in the form of chloride be continuously removed from the reaction system, as takes place upon its conversion into stannic chloride, the reduction of the lead chloridewill proceed to completion. As the stannic chloride volatilizes from the reaction system, additional tin is removed by reaction with the lead chloride, 'and t ere is obtained, in effect, the selective chloridization of the tin from the lead.

In carrying out the above'indicated reaction, the lead alloy containing tin is melted, and the resulting molten bathis skimmed free from oxide products. Lead chloride is charged onto the surface of the bath, the lead chloride being preferably mixed with suitable salts which will lower the melting point of the lead chloride Without entering the reaction. Alkali and alkaline earth chlorides, such as sodium chloride, potassium 3o chloride, and calcium chloride have been employed, and many others may be used-likewise. lThe result is that upon the molten alloy bath there is floating a layer of molten slag, comprising, principally, leadA chloride. A layer of such slag of` considerable depth is allowed to form there being a partial interaction of the tin in the alloy bath with the lead chloride of the slag in accordance with the rst ,y equation above. In

thereby enabling the reaction to run to completion, chlorine gas is passed through the molten slag layer, care being taken to avoid contact between the chlorine and the alloy bath, the latter being stirred vigorously, however, to promote contact between the metal bath and the molten salt slag. During this operation, stannic chloride is evolved freely from the slag, and4 may be condensed and recovered. By maintaining 'the chlorine out of contact with the molten metal bath, formation of lead chloride from the lead is avoided, the lead chloride in the slag being reduced to metallic lead by interfacial reaction with tin in the metal bath, so that in continued commerical operations it is necessary to occasionthe cover 5 by brackets I2 and I3.

any introduce chlorine into the 1ead hath in order to regenerate the lead chloride of the slag layer for replacing that which has been removed by the aforesaid reduction. The chlorination of therslag may be carried out either continuously or intermittently, one of the principal features to be observed, being to maintain the chlorine gas out of contact with the alloy bath except as is necessary` to replenish the chloride content of' Referring more particularly to the' drawing,

and to Fig. l, it will be seen that the materials are received in a receptacle I, which may be of any suitable material such as cast iron, and which may be provided with a ilange 2 for supporting the receptacle I in a suitable furnace 3, provided with one or more burners 4 for melting the charge in the receptacle I. The receptacle I is provided with atightly iitting cover 5 suitably apertured to receive a stirring device 6, a condenser A`I, which is-water cooled, and a tube or pipe 8 for the admissionrof chlorine gas. The stirrer 6 has a stem 9, which is mounted in a bearing I in the cover 5, and also in a bearing II supported on The stem 9 terminates in a pulley I3a, around which is passed a driving belt I4 which is driven from a suitame' motor, not shown.

Thescharge of metal or -alloy from which the tin is to be separated is placed in the receptacle I, as indicated at I5, and this charge is melted. The salts to form the slag layer are distributed over the metaly to form a layer I6 of substantial depth, and because of its lower specic gravity, this layer will float upon the charge of metal. Where the metal charge I5 is a lead-tin alloy, or a lead alloy containing tin, the layer I6 is principally lead chloride, although there may be mixed therewith suitable iiuxing materials,

" chemically inert under the conditions of operations, which will lower the melting point of the salt slag and enable the operations to be carried out at lower temperatures than would be feasible were these fluxes omitted. As indicated above, alkali or alkaline earth chlorides are suitable uxing materials.

When the entire charge in the receptacle I has been melted, the cover 5 is placed in position, and the chlorine inlet 8v and condenser I positioned and connected' to the cover 5, it being understood that all connections are gas-tight to avoid leak- I d age. The chlorine inlet ill dips beneath the salt slag layer I6, but terminates above the metal layer I5, so as to prevent contact between the chlorine entering the charge through the inlet 8 and the metallic layer, I5. Chlorine is gently bubbled through the salt slag layer, the entire charge being maintained molten, and the layer I5 is agitated by stirring with 'the stirrer 6 so as to brlng the metals ofthe layer I5 into contact with the -fusedsalt layer I8. 'Ihe tin in the metallic layer .stannous chloride. suitably agitated, and the-fume evolved during I5 reacts with the lead chloride in the layer I6 to form stannous chloride which remains in the salt slag layer I6, but which is quickly converted into stannic chloride by action of the chlorine bubbling through the salt slag layer I6. The stannic chloride thus produced is volatile at the temperatures of operation, and passes into the condenser 1 where the vapors are condensed, and the resulting liquid stannic chloride recovered. The chlorine may be introduced continuously or intermittently, as desired, in view of the particular operating conditions present.

As a specific illustration of the operation of the present process, it may be mentioned that 500 gms. of lead alloy containing 5% tin were melted in the receptacle I, and the small amount of oxide dross arising from the melting operation was carefully removed. 'To the molten alloy charge were added 448 gms. of lead chloride containing 39 gms. of sodium chloride to suitably lower the melting point of the salt slag. The salt mixture was charged on top of the metallic charge and heated until the entire charge was fully molten.

Chlorine was then gently bubbled through pipe 8, care being taken that chlorine did not enter the metallic layer I5 and to control the bubbling so that the rate of bubbling was such that the chlorine combined substantially entirely with the This metallic layer I5 was the reaction was condensed in the condenser 1, and collected in a suitable receptacle not shown. Practically pure stannic chloride was collected during a period of about one-half hour, which stannic chloride showed by chemical analysis, a tin content of 21.22 gms. of tin. At the end of one-half hour, the rate of evolution of stannic chloride was so small that the chlorination was discontinued. There were recovered 502 gms. of metal from the charge, the excess Weight representing lead entering the charge from the reduction of the lead chloride in the slag during the process. The metal contained only 0.18% of tin. The slag contained 0.55% tin and weighed approximately 450 gms.

V Inanother run, '78% pounds of lead alloy containing 3% of tin were melted in the kettle or receptacle I. To the molten charge was added a salt slag containing 40 pounds of lead chloride, 3.2 pounds of sodium chloride, and 2 pounds of potassium chloride, the temperature being increased until the kentire charge was liquid. The stirrer 6 was introduced into the molten metal, and the cover 2 placed in position on the receptacle I, together with the condenser 1 and chlorine pipe or tube 8, the latter being inserted so that the chlorine entered the slag about one inch above the metal line. During a period of three hours, 2.7 pounds of chlorine were introduced into the molten slag, producing approximately 500 c. c. of stannic chloride. At the end of the run, the metal in the bath weighed slightly more than 76 pounds and contained 0.52%` of tin. The slag weighed 43 pounds, and contained 1.5% of tin.

It will be understood, of course, that the tin content of the recovered stannic chloride may be recovered by any of the well-known operations, or the stannic chloride may be marketed as such, if so desired.

The apparatus shown in Fig. 2 operates similarly to that shown in Fig. 1. .The receptacle I, Fig. 2, may be a cast iron kettleprovided with a ange 2 for supporting the'kettle I in the furnace 3, as described in connection with Fig. 1. One or more burnersl may be employed to heat the furnace 3. The metal charge I is placed in the-receptacle I and melted, anda cylinder I1 is vertically lowered into the receptacle. The lower end I8 of the cylinder is open, and is positioned beneath the surface of the metal charge, theupper end I9 of the cylinder being closed. The end I9 ofthe cylinder I1 is4 adapted to receive a nozzle 2li communicating with a chlorineline 2I coming from a suitable source of chlorine, not shown. The nozzle 20 is restricted at 2Ia to produce a vortex action. A pump 22 is adapted to pump the molten salt slag I 6, as described above, up through pipe 23 and into the nozzle 28, where it is mixed with the incoming chlorine, and the stannous chloride in the slag is thereby converted into stannic chloride, which is then condensed in condenser 1, as above. 'I'he molten salt slag collects in a column 24 in the cylinder I'I until the weight of this column forces the salt slag out through the open end I8 and into the metal charge, the salt slag rising through the metal to the surface thereof, whence it is recirculated by the pump 22 as previously described. As the molten salt slag passes from the open end I8 oi the cylinder I1 upwardly through the metal layer I5, the reduction of the lead chloride 'in the slag by the tin in layer I5 is initiated, the resulting stannous chloride being converted into 'Volatile stannic chloridein the nozzle 20 and cylinder I1. The

`vortex action of the nozzle 28 materially facilitates the `contact between the molten slag and Lthe chlorle entering the nozzle 20 through the pipe 2| th s increasingthe eiiiciency of the con` version of//the stannous chloride into stannic chloride, andtherefore increases the rate at which the tin /i/s removed from the metal bathv I5.

It will be noted that when alloys of lead are being treated for the removal of tin therefrom, it is preferred, of course, to use lead chloride as the active ingredient in the fused salt slag, since such avoids the possibility of introducing any metal other than lead into the metallic bath, it being remembered Athat as the tin is removed from the reaction system, the active chloride is reduced to metal, which enters the metallic bath.J

`So far as concerns the operativeness of the process, however, other chlorides reducible by tin may be employed, such as, for example, chlorides of metals electronegative to tin.

Attention is called to the fact that/the active, ingredient in the slag is selected tofbe such as to be reacted upon by the `metallic constituent in the bath which is to be removed from the bath, the resulting compound of that metallic constituent being removable readily from the reaction system so that the desired conversion and removal can proceed to completion, it being desired to embrace within the scope of this invention such modifications and changes as may be desirable or necessary to adapt it to varying conditions and uses.

. What is claimed is:

1. The process of removing tin from a lead. or alloys of lead containing tin which comprises forming a molten bath thereof, overlying the said bath with a layer of molten slag containing principally lead chloride, contacting the bath and slag until `a reduction by the tin is initiated so that at least a small amount of stannous chloride is included in the slag, passing chlorine gas intothe slag to convert the stannous chloride into stannic chloride intercirculating the slag and the metal bath While continuing to chloridize the slag to maintain reactive interfacial contact between the slag and the bath for maintaining continuously a tin content in the slag, allowing the stannic chloride to volatilize from the slag, thereby substantially completely removing the tin from the bath, /ancl regenerating the chloride content of the -slag as it becomes depleted by periodically introducing chlorine into the metal bath.

2. The process of removing tin from lead or alloys of lead containing tin which comprises forming a molten bath thereof, overlying' the ride to volatilize from the slag, thereby substantially completely removing Athe tin from the bath, intermittently passing chlorine into .the said bath to regenerate the lead chloride content of the slag as it becomes depleted, and condensing and recovering the stannic chloride evolved from the slag.

3. The process of detinning tin-bearing lead and lead alloys which comprises melting the lead and lead alloys in a suitable receptacle under a layer of slag comprising at least relatively large proportions of lead chloride, inserting into the receptacle and through the slag` a reaction vessel having an open end so that the' said open end is below the metal level in the receptacle,

continuously pumping slag from the slaglayer into the reaction vessel while admitting chlorine thereto to intimately contact the slag and chlorine while effecting displacement of metal from the interior ofthe reaction vessel, causing theA chlorine treated slag to pass from the receptacle through the open' end thereof and thence upwardly through the metal layer and in contact therewith, for recirculation through the reaction vessel, and recovering the stannic chloride produced in thereaction vessel.

4. The process of making stannic chloride which comprises continuously circulating molten stannous chloride-bearing material through a reaction vessel lin contact with a stream of chlorine continuously passing into the vessel, intermixing the said materialand the 'chlorine by a vortex action, continuously withdrawing stannic chloride from the reaction vessel, continuously replenishing the stannous chloride content bf the residual material and continuously 'recycling the material through the reaction vessel in contact with fresh quantities of chlorine. f

5. The process of recovering tin from tincontaining metals .such as tin-containing lead and tin-containing lead alloys which comprises melting the metal under a layer slag containing lead chloride under conditions eliecting a partial replacement of the lead of the lead chloride with tin thereby forming stannous chloride in the slag, conning a portion of the slag in a reaction vessel and contacting the said confined slag portion with chlorine to effect a production of stannic chloride, allowing the stannic chloride .to separate from the confined slag portion, passing the said slag portion remaining after the chlorine treatment from `the reaction vessel through the metal to replenish the tin content of the slag, and recirculating the replenished slag y formation of excessive amounts of lead chloride in the slag.

7. A process of detinninglead-tin alloys which comprises forming a molten bath thereof under a slag containing lead tin chlorides, reactively contacting the'slag and bath to cause the slag to pick up tin from the bath while chloridizing the slag to evolve stannic chloride therefrom as the tin enters the slag, and periodically renewing the lead content of the slag as itbecomes depleted thereby maintaining the reactiveness of the slag with respect to the bath while avoiding building up excessive amounts of lead chloride therein.

8. A process of detinning lead-tin alloys which comprises forming a molten bath thereof under a slag containing lead and tin chlorides, continuously reactively contacting the slag and bath to cause the slag to pick up tin from the bath while continuously chloridizing the slag only to evolve stannic chloride therefrom as the tin enters the slag, and occasionally chloridlzing the bath to renew the lead chloride content of the slag as it becomes depleted thereby maintaining the reactiveness of the slag with respect to the bath while avoiding building up excessive amounts of lead chloride therein with consequent depletion of the lead in' the bath.

9. A process for removing tin from lead-tin alloys which comprises forming a molten bath of the alloys, providing a molten slag cover for the bath comprising essentially lead chloride, intercirculating the slag and metal bath to effect a partial conversion of the lead chloride into stannous chloride by reaction at the liquid interface of the slag and metal between lead chloride of the slag and tin in the metal bath, and removing the tin from the slag as stannic chloride by passing controlled amounts of chlorine into the slag only at such a rate that the therefrom.in a fused chloride slag having a high content of lead chloride, removing the tin from the slag bypassing controlled amounts of chlorine into the slag only at such rate that the chlorine combines substantially entirely with the stannous chloride in the slag, and replenishing the tin content of the slag from the tin in the bath being detinned by intercirculating the slag and metal to effect a reaction between lead chloride and tin at the interface between the slag and metal bath while continuing to pass the said controlled amounts of chlorine into the slag.

ll. A process for removing tin from alloys of tin and lead which comprises forming a molten bath of the alloys, extracting tin therefrom in a fused chloride slag having a high content of lead chloride, removing the tin from the slag by passing controlled amounts of chlorine into the slag only at such rate that the chlorine combines substantially entirely with the stannous chloride in the slag, and rplenlshing the -tln content of the slag from the tin in the bath being detinned by intercirculating the slag and metal to effect a reaction between lead chloride and tin at the interface between the slag and metal bath.

12. A process for removing tin from lead-tin alloys which comprises forming a molten bath of the alloys, providing for the bath a molten slag layer comprising essentially lead chloride on the metal bath, reactively contacting the slag and metal bath to effect a partial conversion of the lead chloride into stannous chloride by causing displacement of the lead from the lead chloride.

by tin in the bath, removing the tin from the slag as stannic chloride by passing controlled amounts of chlorine into the slag only at such rate that the chlorine combines substantially entirely with the stannous chloride in the slag, l

intercirculating the metal bath and slag. to replenish the tin content of the slag as the tin is evolved therefrom by effecting interaction between lead chloride and tin at the interfacial surfaces between thebath and slag while continuing to pass the said controlled amounts of chlorine into the slag, and intermittently passing chlorine into the metal bath beneath the slag to regenerate the lead chloride content of the slag.

JESSE O. BETTERTON. ALBERT J. PHILLIPS. 

